In wireless communication systems, wireless communication devices communicate with one or more other wireless communication devices or wireless access points to send and receive data. Typically, a first wireless communication device generates and transmits a radio frequency signal modulated with encoded information. This radio frequency signal is transmitted into a wireless environment and is received by a second wireless communication device. The second wireless communication device demodulates and decodes the received signal to obtain the information. The second wireless communication device may then respond in a similar manner. The wireless communication devices can communicate with each other or with access points using any well-known modulation scheme, including: amplitude modulation (AM), frequency modulation (FM), quadrature amplitude modulation (QAM), phase shift keying (PSK), quadrature phase shift keying (QPSK), and/or orthogonal frequency-division multiplexing (OFDM), and others.
In many wireless communication environments, one of the first or second wireless communication device functions as a base station that provides communication between user devices and a central communication infrastructure. In such a base station, a radio unit is typically positioned at a physically high point of a cellular tower for communication with user devices. However, a significant portion of signal processing actually takes place in a local or remote baseband processor. For example, the baseband processor may be located a significant distance from the radio unit at the top of the tower (e.g., in a bunker underground at the bottom of the tower, or in a nearby communications facility).
In conventional base stations, the baseband processor and the radio unit communicate with one another via a communication link interface. For example, the Common Public Radio Interface (CPRI) provides a standardized interface to connect Radio Equipment Controllers (e.g., baseband processor) and Radio Equipment (e.g., radio unit). Alternatively, the communication link interface may be established utilizing the interface defined in the Open Base Station Architecture Initiative (OBSAI).
CPRI is described in detail in “Common Public Radio Interface (CPRI)—Interface Specification, Version 5.0,” published Sep. 9, 2011, which is incorporated herein by reference in its entirety. OBSAI is described in detail in “Open Base Station Architecture Initiative—BTS System Reference Document, Version 2.0,” and “Open Base Station Architecture Initiative—Reference Point 4 Specification, Version 1.1,” both of which are incorporated herein by reference in their entirety.
In operation, the baseband processor can control the radio unit to communicate with one or more wireless devices via the communication link interface. For example, the baseband processor can timestamp data to be transmitted and then provide the time stamped data to the radio unit. The radio unit can then transmit the data at the time specified in the timestamp. This cooperation between the baseband processor and the radio unit ensures that the data is transmitted at the time specified by the baseband processor, and ultimately at the time specified by the service provider of the wireless communication environment.
The embodiments of the present disclosure will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.